The invention relates to a disc brake, in particular for a commercial vehicle.
In order to maintain a constant running clearance, also referred to as the working travel, between the brake disc and the brake linings in the non-functioning position of the brake linings, that is, in order to compensate for the wear produced by the removal of friction material of the brake linings during braking, a known disc brake is provided, at least on its brake-application side, with an adjustment device. The adjustment device conventionally includes two adjusting spindles which can be rotated synchronously by way of a common drive chain and are thereby axially displaceable toward the brake disc.
In order to detect brake lining wear, use is made of devices consisting of a reduction gear mechanism connected to the two adjusting spindles, and a lining wear sensor connected to the reduction gear mechanism. A device of this type is known from DE 93 12 119 U1.
It is proposed in DE 93 12 119 U1 to use as the brake wear sensor a rotational angle sensor in the form of a rotary potentiometer. The condition of the brake lining is detectable, for example for the driver of the commercial vehicle, via a connected evaluation device.
In order to obtain an accurate indication, the position of the brake lining, i.e., the brake pad, with respect to the positioning of the brake wear sensor must be made very precise, so that careful and precise assembly is required. Naturally, this is possible only with considerable manufacturing cost and complexity, which conflicts with the economical production of a disc brake as a whole.
Furthermore, the replacement of a defective lining wear sensor is also possible only with considerable cost and complexity, especially with regard to the positioning of the lining wear sensor in relation to the brake lining and to the position of the reduction gear mechanism. An exchange of the lining wear sensor can therefore be carried out only by appropriately trained personnel, which, however, again conflicts with the desirability of lowering the operating costs.
It is therefore the object of the invention to develop a disc brake that can be assembled in a simpler and more economical manner and that have a lining wear sensor that can be exchanged without difficulty.
This and other objects are achieved by a disc brake, in particular for a commercial vehicle, having a brake caliper which engages over a brake disc, brake linings which contact the brake disc in an operating position, a brake application device with which one of the brake linings can be pressed against the brake disc via at least one adjusting spindle, and a wear adjustment device which is connected in a rotationally fixed manner to the adjusting spindle and with which a wear-induced change in a running clearance between the brake lining and the brake disc can be substantially compensated. A closure lid covers the wear-adjustment device and is fastened to the brake caliper. A lining wear sensor communicates with a reduction gear mechanism connected to the adjusting spindle. Connected to the reduction gear mechanism is a transmitter revolving on a concentric path and communicating with the lining wear sensor. The lining wear sensor is operatively configured as a contactless sensor by which a change in the angular position of the transmitter is detectable and transmittable to an evaluation device.
This design configuration produces advantageously a constructional separation of the lining wear sensor and the reduction gear mechanism; that is, the two elements are no longer physically connected to one another.
As a result, there are a large number of advantages; in particular, the invention provides a disc brake design of minimal complexity and cost.
For example, according to the invention, it becomes possible to have an automated assembly, since the reduction gear mechanism, the chain and the chain wheels which can be fitted to the respective adjusting spindles, can be combined and installed practically as a constructional unit. The closure lid then need only be fitted and screwed to the brake caliper. The lining wear sensor is then fastened to the outside of the closure lid, in which case the reduction gear mechanism and the lining wear sensor are preferably separated by a wall of the closure lid.
Isolation of the reduction gear mechanism and the chain from the outside region is thereby achieved. The lining wear sensor can therefore be installed and removed without intervention in the reduction gear mechanism, while the wear of the brake lining can be detected by the lining wear sensor in conjunction with the transmitter, depending on the position of the transmitter, which is also covered by the closure lid.
However, as already known from the prior art, a precondition for such detection is that the reduction gear mechanism, for example in the form of an epicyclic gear, is designed in such a manner that a rotation of the transmitter does not exceed 360°, preferably 300°, over the full wear travel. That is to say that while the adjusting spindle performs, for example, seven revolutions in order to compensate for the maximum wear travel, the transmitter rotates only once through not more than 300°.
In order to ensure unimpeded communication between the transmitter and the lining wear sensor, the transmitter rests without free play against the wall of the closure lid while the lining wear sensor bears without a gap against the opposite side of the wall.
The transmitter is preferably pressed against the wall of the closure lid under spring loading, for which purpose a compression spring is arranged in a hollow wheel of the epicyclic gear, the other end of the compression spring bearing against a planet wheel carrier. A carrier wheel to which the transmitter is fastened is retained in a rotationally fixed manner on the hollow wheel. Through the arrangement of the compression spring in the hollow wheel, an extremely low overall installed height of the reduction gear mechanism is achieved, complying with the requirement for a compact structure of the disc brake.
As a contactless sensor, the lining wear sensor may vary in construction and in operating principle. For example, the functional unit of the contactless sensor/transmitter may operate on a magnetic basis or inductively. It is also possible to implement the contactless sensor in the form of a transponder.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.